1. Field of the Invention
The present invention relates to the formation of high contrast black images on substrates by dry peel-apart imaging processes. Of particular importance to the practice of the present invention is the fabrication of a high contrast black image on a transparent substrate, particularly in a process for generating a black matrix (BM) for use on an emissive display panel such as a liquid crystal display (LCD) panel, most importantly for use in the manufacture of a color filter (CF) for a (flat panel) display device.
2. Background of the Art
Display devices, and particularly flat panel display devices such as those using emissive arrays such as liquid crystal panels, require the use of a color filter layer to form the desired image to be viewed from the display. A color filter, in its simplest description, is a fixed image of color through which light is passed to display the image when desired. The actuality of the color filter is more complex, with multiple requirements of high image resolution, sharp image features, physical durability and light stability of the image, often static resistance, and also thermal resistance being needed. The color filter has traditionally been constructed of a black matrix (a black border) which outlines and separates the color portions of the image) and the color portions of the image through which light is passed to project the image, the light often being generated by a radiation emitter such as a liquid crystal display, phosphor display, and the like. The black matrix has been important because it acts to separate colors so that they do not mix or blend and so that sharp image features can be presented. It also prevents white light from leaking through the separation between color elements, thereby maintaining high color saturation in the display. The function of the black matrix requires that the lines are even, sharp and have high resolution and image density so that colors laid down next to (and often slightly overlapping) the black matrix lines do not appear in the projected image.
One method of making colored images upon a non-photosensitive base uses laser induced colorant transfer or laser induced mask production. A donor element is induced (as by ablative levels of radiation) to transfer donor color material to a receptor surface. The donor may contain radiation or thermally sensitive materials to enhance the efficiency of transfer, or the donor material may be ablated without additional materials. Examples of this type of imaging process includes U.S. Pat. Nos. 5,156,938, 5,171,650, 5,256,506, and 5,089,372. The first three patents generally refer to producing a pattern of intelligence.
U.S. Pat. No. 5,171,650 particularly discloses methods and materials for thermal imaging using an "ablation-transfer" technique. The donor element for that imaging process comprises a support, an intermediate dynamic release layer, and an ablative carrier topcoat. The topcoat carries the colorant. The dynamic release layer may also contain infrared-absorbing (light to heat conversion) dyes or pigments. The pigments also include black copper as an additive. Nitrocellulose is disclosed as a possible binder.
Copending U.S. application Ser. No. 07/855,799 discloses ablative imaging elements comprising a substrate coated on a portion thereof with an energy sensitive layer comprising a glycidyl azide polymer in combination with a radiation absorber. Demonstrated imaging sources included infrared, visible, and ultraviolet lasers. Solid state lasers were disclosed as exposure sources, although laser diodes were not specifically mentioned. This application is primarily concerned with the formation of relief printing plates and lithographic plates by ablation of the energy sensitive layer. No specific mention of utility for thermal mass transfer was made.
U.S. Pat. No. 5,308,737 discloses the use of black metal layers on polymeric substrates with gas-producing polymer layers which generate relatively high volumes of gas when irradiated. The black metal (e.g., aluminum) absorbs the radiation efficiently and converts it to heat for the gas-generating materials. It is observed in the examples that in some cases the black metal was eliminated from the substrate, leaving a positive image on the substrate. This type of system, with or without the gas generating polymer, has been suggested for use in the formation of black matrix materials, by transfer or ablation.
U.S. Pat. No. 5,278,023 discloses laser-addressable thermal transfer materials for producing color proofs, printing plates, films, printed circuit boards, and other media. The materials contain a substrate coated thereon with a propellant layer wherein the propellant layer contains a material capable of producing nitrogen (N.sub.2) gas at a temperature of preferably less than about 300.degree. C.; a radiation absorber; and a thermal mass transfer material. The thermal mass transfer material may be incorporated into the propellant layer or in an additional layer coated onto the propellant layer. The radiation absorber may be employed in one of the above-disclosed layers or in a separate layer in order to achieve localized heating with an electromagnetic energy source, such as a laser. Upon laser induced heating, the transfer material is propelled to the receptor by the rapid expansion of gas. The thermal mass transfer material may contain, for example, pigments, toner particles, resins, metal particles, monomers, polymers, dyes, or combinations thereof. Also disclosed is a process for forming an image as well as an imaged article made thereby.
A series of patents (U.S. Pat. Nos. 4,965,242, 4,962,081, 4,975,410, 4,923,860, 5,073,534, and 5,166,126) have been assigned to Kodak disclosing the use of thermal dye diffusion transfer to make filter elements and color filter constructions. U.S. Pat. Nos. 4,965,242 and 5,073,534 teach the use of high T.sub.g polycarbonate and polyester receiving layers to accept the thermally transferred dye. With both receiving layers, a vaporous solvent treatment is required to drive the dye into the receiving layer.
U.S. patent application Ser. No. 08/273,419, relates to a process of forming a black matrix with a color filter element within the matrix. The process may generally involve the following steps:
1) provide a light transmissive substrate having a thermally transparentizable (e.g., any process which generates heat to remove materials, including photochemical processes in which irradiation causes chemical changes which effectively transparentize the coating) black coating thereon, PA1 2) projecting radiation against said black coating to transparentize black coating on said substrate, said transparentization creating areas on said substrate which are more light transmissive than areas where black coating has not been transparentized, and PA1 3) transferring one or more pigment layers onto at least some of said areas which are more light transmissive to create a black matrix/color filter element. PA1 (A) providing a photosensitive element comprising a transparent support, a subbing layer, a photosensitive layer comprising (polymeric binder, colorant, photoinitiator system, and photopolymerizable ethylenically unsaturated monomer, with the weight ration of monomer/binder being at least 4:1), and an adhesive layer comprising a thermoplastic polymer with a T.sub.g between 20.degree. C. and 100.degree. C., PA1 (B) either (i) providing a receiver base and laminating the receiver base at elevated temperature to the adhesive layer and then imagewise exposing the photosensitive layer, or (ii) imagewise exposing said photosensitive element to actinic radiation, and then providing a receiver base and laminating the receiver base at elevated temperature to the adhesive layer, PA1 (C) peeling apart said transparent layer and said receiver base whereby the adhesive layer and the imagewise exposed areas of said photosensitive layer are transferred to the receiver base. Steps (A) through (C) may be repeated to provide multicolor images. PA1 a) a carrier layer, b) a pigmented black color photohardenable layer (referred to herein as the "PPa" layer), c) a photopolymeric adhesive layer (referred to herein as a "PPl" layer), and an optionally preferred strippable liner layer. The viscosity of the unexposed photopolymer adhesive layer must be below 100,000 cps at 25.degree. C. (if the lamination and peel apart process is performed at that temperature, or below that 100,000 limit at the temperature at which the lamination and peel apart process is actually performed, e.g., up to 50 degrees Centigrade) to avoid premature delamination of the PPa layer from the carrier layer.
WO 96/10215 (PCT/EP95/03423) describes a method for the formation of a negative color image comprising the following steps in order:
WO 96/10216 shows processes similar to those of WO 96/10215 except that by control of the monomer to binder ratio, either positive or negative images may be transferred to a receiver base.
UK Patent Application GB 2 129 952 A describes a peel imaging system comprising a first carrier sheet, a photopolymerizable layer (containing a non-attenuating, non-photosensitive dye or pigment and contains material which changes color when exposed to actinic radiation), and a second carrier sheet, at least the first carrier sheet being transparent or translucent, the photopolymerizable layer both polymerizing and changing color upon exposure to actinic radiation. After peeling apart of the carrier, the photopolymerizable material shears along the edges of the imaged areas so that exposed areas of the photopolymerizable layer remain on the first carrier sheet.
U.S. Pat. No. 4,288,525 describes a photosensitive material which may be used in peel-apart imaging processes, particularly in the formation of dry transfer materials, resist masks, printing plates and silk screen stencils. The imaging material consists of two carrier sheets which may be peeled apart and which are laminated together via at least two interlayers (a photosensitive layer and an image forming layer). Prior to exposure, if the carrier sheets are peeled apart, the carrier sheet adjacent the photosensitive layer separates wholly from it, leaving both photosensitive layer and image forming layer on the other carrier sheet. After exposure, if the sheets are peeled apart, the whole of the photosensitive layer and at least part of the image forming layer (according to its imagewise exposure) remains attached to the carrier sheet adjacent the photosensitive layer. By incorporating adhesive in or adjacent the shearable image forming layer, the photosensitive material may constitute a material from which dry transfers may be manufactured simply by exposure and peeling apart.
EPO Application No. EP 0 323 191 A2 describes a peel-apart imaging material useful in image transfer processes. The imaging material comprises a substrate and a photosensitive layer, the photosensitive layer (as two or more layers) comprising a dye or pigment and a photopolymerizable compound. The dye or pigment is contained in at least one of these two or more layers, but is absent from the layer in direct contact with the substrate. Upon imagewise exposure of the image forming material, the exposed and unexposed areas differ in their adhesion to a receptor and image transfer occurs through a breakaway separation within the layer in direct contact with the substrate.
WO 93/03928 describes peel-apart elements for laser induced thermal imaging processes, the elements comprising, in order, a support, an active layer (infrared absorbing material, and polymeric binder), an adhesive layer, and a cover sheet. The adhesive interrelationship between layers are such that upon peeling the layers apart, regions of the active layer exposed with infrared radiation adhere to the support while exposed regions adhere to the adhesive layer and the cover sheet, forming a negative image and a positive image on the respective sheets.
EPO Applications 0 096 572 A2; 0 385 466 A2; and 0 601 760 A2 and U.S. Pat. Nos. 4,050,936; 4,347,300; 4,291,114; 5,001,036; 5,234,790; 5,300,399; and 5,374,780 also describe peel-apart photosensitive imaging systems with adhesive layers.